The absolute minimum latency you'll ever see with geostationary is about 489ms. That's assuming 1:1 dedicated transponder capacity and something like a higher end SCPC terminal and modem, accounting for latency and modulation/coding/FEC by the satellite modems on both ends.
Consumer grade hughesnet stuff will vary anywhere from 495ms in the middle of the night to 1100ms+ during peak periods due to oversubscription.
This should probably tell you something about spacex's claims as well. The actual latency is never just the slant range. There's a ton of processing and network switching too.
I am pretty optimistic about SpaceX's claims for what the space-segment latency will be. If you look at the system architecture for current generation high-bandwidth Ka-band geostationary services, which has dozens of spot beams on North America, there's about 30 teleports spread out around the US and Canada. These allow Viasat and Hughesnet customers, and similar, to consume capacity in the same spot beam as the teleport they're uplinked from (vs the satellite cross-linking a set of kHz from one Ka-band spot beam to another). For example, customers in really rural areas of Wyoming are going to connect to a teleport that's in Cheyenne, which will usually be in the same spot beam. Sites in Cheyenne near the railway have really good terrestrial fiber capacity for an earth station operator to buy N x 10 or 100GbE L2 transport links to the nearest major city.
It would be technically possible, but uneconomical and an inefficient use of space segment transponder kHz to have customers in Wyoming moving traffic through a teleport in the Chicago area. Here's an illustration of Ka-band spot beams on a typical state of the art geostationary satellite:
Applying the same concept to starlink, telesat's proposed system, and oneweb, if they build a number of teleports geographically distributed near rural areas, it will allow individual satellites to serve as bent-pipe architecture from CPE --> Teleport, within the same moving LEO spot beams, or to have customer traffic take only one hop through space to an adjacent satellite before it hits the trunk link to an earth station. For example customers in a really rural area of north Idaho along US95 might "see" a set of moving satellites that also have visibility to an earth station in Lewiston, ID, where carrier grade terrestrial fiber links are available. Or a customer in a remote mountainous area of eastern Oregon may uplink/downlink through a teleport in Bend.
The ultimate capacity of the system will be determined by how few hops through space they can get the traffic to do. Since every satellite will be identical and capable of forming a trunk link to a starlink-operated earth station, when it's overhead of it, they have an incentive to build a large number of earth stations geographically distributed around the world.
It's basically the same idea as o3b's architecture but at a much smaller scale.
I don't doubt the latency in space numbers. What I don't believe is using a theoretical distance to compute latency. As you said, a LOT of that latency can come from scheduling inefficiencies and congestion. Each of their satellites has a relatively small amount of bandwidth, so if you happen to be in a beam with a lot of people, you'll be hit hard by this. As far as I know, their satellites are not capable of steering beams, and rely purely on the placement directly down from where they are.
Another consideration: adding another 50ms to GEO latency isn't really going to change anyone's opinion. It's still targeted towards streaming, and latency doesn't matter as much since they're not targeting real-time gamers. SpaceX needs the latency to be very low to hit that market. There's a world of difference going from a 30ms ping to an 80ms ping, and once you're past a certain point, it puts you in the same camp as GEO.
> As far as I know, their satellites are not capable of steering beams, and rely purely on the placement directly down from where they are
This is wrong. From their FCC filing(1), they use AESA phased array antennaes, and each satellite is capable of simultaneously maintaining "many" (unspecified) steered beams that are <2.5 degree wide.
Also, the receiver is capable of distinguishing between multiple beams covering it so long as there is more than 10 degrees of angular separation between them from it's point of view. If I understood it correctly, this will allow nearly every visible satellite at the same orbital height (less the ones very nearest to horizon) to communicate with targets that are geographically very near to each other at full bandwidth. After the very first phase has been launched, they can provide a total of ~500 Gbps of downlink bandwidth to any spot target that lies between 40 and 60 degrees latitude. The later additions at high orbits help with total capacity and especially with targeting multiple targets relatively near each other, but do not help provide more bandwidth per city, as that is limited by the 10 degree angular separation requirement.
The VLEO (330km-ish) constellation will help with that by reducing the size of each spot.
one noteworthy item from the filing is that they intend to build 200 Gateway earth stations just within the continental United States, which means that the vast majority of satellites will be functioning as Bent pipe repeaters. I don't think that there will be a lot of traffic traveling satellite to satellite in a multiple hop arrangement. 200 sites for their ka band trunk links from satellite to earth station means that a CPE terminal in, for example rural NW Montana might have a 25-30ms latency to a gateway in Spokane, and from there the latency to internet destinations will be all fiber based, same as any existing ISP.
if I had to guess on the earth station siting, they are picking locations which are medium-sized cities with decent terrestrial fiber connectivity, which will be within the same satellite view footprint as adjacent rural areas. Such as an earth station in Boise may serve mountainous remote areas of ID.
This 200 Earth station figure also lends me to believe that the first manufacturing run of satellites may not have any satellite to satellite trunk link ability at all, but that they will ALL be bent pipe architecture. this means that if SpaceX wants to serve a particular area, they need to have an earth station on terrestrial fiber in the same region, which is simultaneously visible to satellites and end users.
I think that's a very good observation, especially given the recent news that as part of musk firing some of the leadership on the project, he wants the satellites to be significantly simpler.
If that's the case then the problem becomes exponentially more complex than I was thinking, and the technical challenges are going to be far harder than I'd first thought. Doing frequency reuse and interference mitigation at the rates they need to if they're going to steer the beams is enormously complex.
I'm in agreement about the technical challenge - doing it with "low cost" phased array CPE is challenging. If I had to engineer it I'd design something with a pair of highly shielded, tight focal axis parabolic antennas (basically a miniaturized o3b terminal), like two 60cm size on two-axis tracking motorized mounts. But there's no way that sort of setup with a unique rf chain for each of two dishes would be under $5000.
Even if it is 150-250ms to terrestrial internet connections, it will be a lot better than consumer grade geostationary. The unfortunate economics of launching 3500-6000kg things into geostationary orbit means that transponder capacity on current satellites used for consumer grade VSAT services are horribly oversubscribed. You're not going to get very good satellite service with the current cost structure and tech for $80 to $150/mo on a 3 year contract. One needs to look at figures like $400-500/mo, and a 1.8m size antenna for more complex modulation, before vsat access is really "good".
If the space segment only adds 120ms to what would be an otherwise same latency rtt ping, it's not so bad, people in the US have been spoiled by having CDNs very near all major ix points.
I disagree with that. I think there's a latency line that if you exceed that, certain functions are no longer possible. Real-timing gaming is one of those, and VoIP as well with a slightly higher latency. You are at a complete disadvantage playing real-time games if your ping is 150ms compared to someone else at 30ms, to the point where you may as well not play those types of games.
I'm not sure what the justification is to assume that Starlink will not be horribly oversubscribed, either. Last I checked it was supposed to be about 32Tbps with all satellites operational. A substantial amount of that is completely wasted over water, so the effective capacity for customer that actually have the money for SpaceX to generate revenue is very small. The types of services people need in remote areas, whether it be a plane or in a village that has never had internet are not those that require low latency. They are either streaming media (plane), or web browsing. In that sense, I don't see how Starlink has and advantage there.
I would be shocked if they could deliver something better than cable on DOCSIS 3 to even 10% of cable customers with comparable service. My guess is it will be tailored more to high-paying customers that happen to not be able to get decent cable.
Probably will be radically oversubscribed in order for the economics to work, and will be a shittier service than a properly implemented vdsl2, g.fast or docsis3/3.1 last mile (nevermind gigabit class gpon or active Ethernet ftth), but significantly better than small geostationary service vsat. And will be higher latency and with worse GB/mo bandwidth quotas compared to a modern technology WISP for last mile.
A lot of the technology press has misunderstood the most desirable applications and locations for it. People think that it's going to compete for a residential internet service in a suburb of a city like Portland, or Sacramento, or Denver. If you can get 300 megabit per second DOCSIS3 service in one of those locations, that would be drastically better. where it is going to be a game-changer is all of the locations that are right now dependent on highly oversubscribed geostationary small vsat services, and extremely rural areas where there isn't even a single last-mile terrestrial Wireless ISP. and for ships in the middle of the ocean, if the gigabyte per dollar cost is significantly less than inmarsat or other options.
I think I understand what you are saying, but I'm confused at this comment compared to your others. If you believe, as I do, that the user terminal is going to be extremely expensive, how will that compete with the current small vsat terminals?
I agree that the service could be better in theory, but at the same time, existing satellite internet service also could be better by taking on fewer customers and not being as congested. But that's a cost trade-off. And in this case, I believe SpaceX has a higher cost per customer to recoup, so it seems in their best interest to also be congested to increase revenue.
I think that there is a good chance the terminal will be expensive, but the cost hidden or eaten by spacex to gain market share. Building a phased array thing with sufficient gain that can track two LEO satellites can't be cheap. But maybe their terminal hardware engineers have come up with something truly revolutionary, and we will all be surprised. I am hoping but skeptical that it could have similar hardware costs to a viasat small ka-band vsat terminal, in the range of $800-900 for rooftop equipment + modem.
> Last I checked it was supposed to be about 32Tbps with all satellites operational.
It will be ~80Tbps after the first three phases (the LEO constellation), ~240Tbps after VLEO.
I agree with you that they probably cannot offer enough bandwidth to compete with residential internet in densely habited areas.(1) The system is really interesting in less densely inhabited places, and for backhaul. The complete system has more transcontinental bandwith between almost any two (distant enough) places than all submarine cables between them put together. This alone will likely pay for the whole system, with plenty to spare.
(1) With a few exceptions. After the full constellation is up, New Zealand will have ~30 times more downlink capacity than the entire bandwidth use of the country as of right now, and will also have tens of times more connecting capacity with North America and Australia than it currently has. But that requires a country of only 6 million in the starlink sweet spot that gets all of the bandwidth of all visible satellites to the east of it.
I agree. I think the capacity on paper is very impressive, and the trans-continental capacity will be useful. I'm just more skeptical that they'll find a market willing to pay the price it will cost easily in the residential market. Satellite internet is more expensive than cable, and I don't see any way that will change considering their hardware will be more expensive than the current satellite internet hardware (just based on phased array). 1Gbps cable isn't unheard of these days, but the question is whether there's really a market for it. At some point you are past a speed where it has any material effect on what you're doing, and SX needs a small amount of customers paying a large amount of money due to the equipment costs. What they can't have is lots of customers with 50Mbps plans that have identical equipment to someone paying 10x more for 1Gbps.
Consumer grade hughesnet stuff will vary anywhere from 495ms in the middle of the night to 1100ms+ during peak periods due to oversubscription.